This invention relates generally to systems that provide graphics environments for application programs, and more particularly to communication between application programs in systems capable of running multiple application programs written for various environments.
In modern data processing, protocols define the data formats and order of communication that allow application programs to communicate with system components such as I/O devices or servers. These protocols include application programming interfaces, interprocess communication protocols, and remote procedure calls. With the rapid growth of computers and application programs, there has been a parallel growth in the number of software and hardware protocols. The existence of multiple protocols throughout the data processing industry has been a source of inconvenience because application programs written for one protocol must be modified, rewritten, or even redesigned, for a different protocol.
The problem of multiple protocols is particularly acute in the graphics area where there are a number of standards in use. Certain graphics systems use a software package called a display server to implement a graphics protocol. In such systems, application programs requesting graphics services, called clients, send their graphics requests to the display server.
The graphic services can include an interclient communication facility. As discussed in greater detail below, interclient communication may be required when, for example, a user copies text from a window "owned" by one client into a window owned by a different client. Windows are areas on a video screen that allow a user to view data processing output. Windows provide clients an organized way of managing the use of space on the screen, and allow the display server to present information for multiple clients in an organized way.
It is often desirable for different display servers, each with their own set of clients, to run on the same system. If this is done, there is often a need for clients connected to one server to communicate with clients connected to the other server. For example, a user may wish to copy data from a window generated by one server into a window generated by another server.
FIG. 1 is a diagram of a system disclosed in U.S. Pat. No. 4,899,136 having a server implemented by a host system processor and another server implemented by an emulating processor. When a user copies data from a window generated by the host system processor into a window generated by the emulating processor, the host processor seizes control of the keyboard buffer for the emulating processor and writes the data into the buffer by simulating key strokes.
One problem with this method of communication is that in order to transfer data in this manner, the host system processor must have access to low-level data structures of the emulating processor, such as keyboard buffers. Writing a system having this architecture is inconvenient.
Converting an existing single server system into such a system, may also entail substantial legal and technological problems. For example, the person attempting to implement such a system might not possess the legal right to modify the support technology used by an existing single server system, as that technology may be protected by the intellectual property rights of another. Also, the support technology of the single server system may be poorly documented or structured in such a way as to make it difficult or impossible to adapt to support another server. Therefore, it is desirable not to have to modify existing host systems.
Further, the '136 patent's method of data transfer is limited to types of data that are represented by key strokes, and may therefore not be suitable for the bidirectional transfer of other data, such as bit-map data. Also, the '136 patent only provides for the transfer of bit-map data from an emulating processor window into a host system processor window, but not for the transfer of data from a host system processor window into an emulating processor window.
An example of a single server graphics system having a communication facility common to a number of clients is one defined by the X Window System protocol, a standard developed at the Massachusetts Institute of Technology. FIG. 2 shows an X Window system, where clients 210, 220, and 230 send graphics request to a display server for implementing the X Window System Protocol (X server) 240, thereby communicating with graphics hardware 250.
Basic principles and architecture of the X Window System may be found in "Introduction to the X Window System" by Oliver Jones, Prentice-Hall 1989. The protocol for communicating with an X Window display server is described in "X Window System Protocol MIT X Consortium Standard X Version 11," Release 4, by Robert W. Scheifler, MIT Laboratory for Computer Science. Conventions for communication between clients are described in "Inter-Client Communication Conventions Manual, Version 1.0, MIT X Consortium Standard," by David S. H. Rosenthal, Sun Microsystems, Inc.
X Window Systems are not the only graphics systems in use throughout the industry. Therefore, it may be desirable to execute clients written for an X Window System together with clients written for some other type of windowing system. An example of another windowing system currently in use is the Microsoft Operating System/2 Presentation Manager (PM). It is therefore likely that a need will arise to execute clients using the X Window System protocol (X clients) in the same system as clients using the PM system protocol (PM clients).
When using the two different types of clients in a single system as described above, it is desirable to allow X clients connected to the X server to communicate with PM clients connected to the PM display server (PM server), thereby allowing the user to transfer text or other data from a window owned by an X client into a window owned by a PM client.
Further, it is desirable that an X client be able to communicate with PM clients in the same manner as the X client communicates with other X clients, while allowing a PM client to communicate with X clients in the same manner as the PM client communicates with other PM clients.